Yes, pet fish does remember us. The study claims that fish are sentient beings with intelligence, self-awareness and can experience emotions like fear, happiness, and pain. The study was done by giving the fish an electric shock which made them fearful of getting into the area where they got shocked before. So basically over time, you will see the fish having longer times to stay far away from these areas… It is likely that your pet fish has shown signs of stress when you left him alone for some days… But do remember that cories are shoaling fishes so it is not good to keep them alone…
Fish don’t just react to painful stimuli but can also experience fear and stress—and perhaps even physical pain—accordingly new Australian research suggests.
The study provides evidence fish have nociceptors — specialized nerve cells that sense noxious or harmful events — which respond to damaging stimuli by sending signals to the brain.
“There are so many studies showing nociception in fish, but no one has demonstrated pain,” said study co-author Joseph Garner, an associate professor of biological sciences at the University of Utah. “This is the first time it has been demonstrated that fish have pain.” Scientists had assumed fish could feel physical pain because when they are hurt they respond physiologically much as mammals do—they secrete hormones that trigger changes in blood chemistry and physiological activities to ease stress. However, until now there was no direct evidence for this. The new findings don’t mean the fishing is now off-limits but suggest anglers should take care not to damage their catches any more than necessary when removing the hook.
Garner and colleagues from the University of Queensland gave bee venom injections to the lips or hand of 22 volunteers—to simulate a fishhook barb puncturing their skin—and then exposed them to chili powder, which causes burning pain. They asked them how painful it would be for a 10-year-old child, and also asked the volunteers to rate changes in their stress levels. This confirmed that they could judge fairly accurately whether others were experiencing pain or fear because they had been through a similar experience themselves. The team also determined that goldfish experienced pain by pinching their mouths until they opened them, causing them discomfort, so much so that many stopped eating even though were hungry. “The goldfish treated with the bee venom could not eat for about 10 days. It was so severe I decided to sacrifice the fish after six days because it caused pain,” Garner said.
The scientists also tested whether goldfish had memory by conditioning them to push a lever to turn on a light inside their tank, which simulated “positive reinforcement” that occurs when animals are trained by reward. The team then shut off the power source for eight hours—making it impossible for them to get the reward—after letting the fish recover overnight by turning on the machine again. At first, they made many attempts in vain because they simply forgot what they were supposed to do, but after four days of training, guided by their memory of pushing levers rather than hunger, they began remembering.
To test memory further, the team shut off the power supply to the fish tank four times a day for periods of six minutes each—and found that after 19 days, they remembered pushing levers even in advance by one day to turn on lights when another period of training would be interrupted. “This is very much like when humans learn something and remember it later,” Garner said. “Fish can recognize novel things when they experience them.”